The invention relates to an arrangement for a non-hermetic seal between a stator and a rotor of a turbomachine.
The term “turbomachines” refers to power-absorbing and power-generating, bladed fluid-flow machines with stator and rotor, such as compressors, pumps and turbines. The invention is directed in particular toward gas turbines in an at least partly axial type of construction for mobile and stationary applications; however, it may also be of interest for steam turbines for example. In practical terms, this involves the sealing region between guide blades and rotor radially inside the actual flow passage. In gas turbine technology, this region is frequently referred to as Inner Air Seal (IAS).
German Patent Document No. DE 196 28 559 A1 describes an arrangement of the generic type for the inner air seal, comprising a brush sealing ring which belongs to the stator, is mounted on the guide blade roots by a spoke centering means and forms together with a cylindrical rotor surface a fluid barrier which is permeable in a defined manner. The principle of the spoke centering results in advantages where marked relative dimensional changes occur between coaxially arranged, connected components due to thermal effects. Since the thermal loading and the heat capacity of adjacent components can be very different, one component, for example, expands earlier, quicker or to a greater extent than another, adjoining component. A spoke centering means comprises at least three support points uniformly distributed over the component periphery and having in each case radial relative mobility. In this case, it is assumed that the components expand and contract uniformly, that is to say dimensional changes take place essentially without changes in shape. In many applications, this is at least approximately the case, support clearances and elasticity compensating for small deviations. The support points with a translatory degree of freedom may be designed, for example, as a combination of sliding block/groove or pin/bush. Components connected by spoke centering are rotationally secured relative to one another and remain concentric during relative dimensional changes (circumference, diameter). Relative axial fixing can in this case likewise be realized.
In the embodiment according to German Patent Document No. DE 196 28 559 A1, there is, for example, a contact element (9) in the form of a rim or bead on the side of lower operating pressure, against which contact element (9) the brush sealing ring (items 1, 2) is pressed and which also performs a sealing function. The contact element (9) seals off an end face of the brush sealing ring at the radially outer margin, so that the operating pressure difference is effective on a large part of the end face of the brush sealing ring. The area effective in this case extends radially from the rotating sealing surface on the inner part (3) up to the contact element (9). The product of pressure difference and effective area may lead to a considerable axial force on the brush sealing ring and ultimately the contact element. In combination with the radial relative movements, which occur cyclically, between the brush sealing ring (item 1) and the contact element (9), this results in high friction and wear (fretting, etc.). In the inner air seal, the situation is generally such that the guide blades suspended on the casing radially on the outside, when hot gas is admitted, “grow” radially inward, i.e., toward the brush sealing ring, and “retract” again radially outward during cooling. This takes place during every thermal loading and load-relief. Apart from friction and wear, the “free” centering may also be impaired, so that the brush sealing ring is possibly deformed, and thus the sealing effect is changed.
Against this background, the object of the invention is to provide an arrangement for a non-hermetic seal between a ring-shaped guide blade cascade and a rotor of a turbomachine which is at least partly of an axial type of construction, which arrangement, with applications of the principle of the spoke-centered brush seal, results in marked improvements by a reduction in friction and wear, by centering free of constraining force, and by a reduction in the secondary leakage in the region of the axial contact surface of the brush sealing ring.
As a sealing contact element for the bristles on the side of lower operating pressure, a supporting ring is arranged in the radial vicinity of the rotating sealing surface, this supporting ring being integrally connected to the guide blade roots and therefore no longer being a component of the brush sealing ring. In combination with a design of the spoke centering means permeable to pressure, the arrangement is pressure-relieved axially to the greatest possible extent and is therefore free of force, since the operating pressure difference is only effective in the region of the small, annular bristle area between rotor and supporting ring. Since the bristle wear to be expected on the supporting ring is low and is probably more likely to be less than the wear on the rotating sealing surface, the last-mentioned type of wear should remain the criterion for an exchange of the brush sealing ring. It is assumed that, over and above the exchange of the brush sealing ring, relevant maintenance measures will not be necessary either on the rotor or on the guide blade roots, including supporting ring. Depending on whether the guide blades of a ring are all integrally connected or are arranged in segments or as individual parts, the supporting ring will also be designed in one piece or so as to be interrupted by parting seams, that is to say, segmented. Individual guide blades or segments of a small number of blades may twist slightly elastically about an—imaginary—radial axis during operation, so that the supporting ring segments on the guide blade roots no longer form an optimally plane contact surface but a contact surface which is slightly stepped at the parting seams. This will be elastically compensated for by the bristles without impairing the sealing effect. It may be noted that, in arrangements according to the prior art (see, inter alia, German Patent Document No. DE 196 28 559 A1), undesirable leakage flows (secondary leakage) of a relevant order of magnitude may occur between twisted contact segments and the rigid brush carrier.